Optical devices are used in combination with other elements in optical communication systems. It is generally necessary to provide connections to the devices for the input or output of optical power. In order to facilitate the making of these connections it is advantageous to mount the optical device on a support member.
The nature of many optical devices, for instance semiconductor stripe lasers is that, in use, the optical activity with which the device is concerned is located in a longitudinal volume extending the length of the device. Input or output of optical power to or from the device must be made at an end of the longitudinal volume. In a number of applications of such devices a port for input or output of optical power is necessary at both ends of the longitudinal volume. Any support member on which the device is mounted for use in these applications must therefore be designed to allow access to both ends.
We have observed that the quality of optical signal achieved can be impaired by its transmission into or out of the device concerned and that this can present serious difficulties. In particular, if the deivce is mounted on a face of a support member which extends beyond either end of the device's longitudinal volume, partial reflection of the signal can occur at the face of the support member. Subsequent interference between reflected and unreflected components of the signal can then cause fluctuations of amplitude and phase distrubance. It can therefore be important that the support member face does not extend beyond the ends of the longitudinal volume of an optical device.
Two further factors which can influence the design of a support member are firstly the fragility of optical devices and secondly the potential function of the support member as a heat sink.
Taking the first factor; because an optical device is fragile, to be efficient the support member should support it throughout its length, that is from end to end. Taking the second factor; active optical devices may tend to generate unwelcome heat during use. For instance, in semiconductor stripe lasers, which generate heat in use, an increase in temperature of the laser material leads to an increase in the input of current threshold at which it will start to lase. The higher input current required in turn leads to a further rise in temperature. Hence, the support member can play an important role by conducting heat away from the optical device. To do this efficiently, it is important that the support member is in conact with the optical device concerned throughout the latter's length.
Optical devices, however, can vary considerably in length. For instance, a semiconductor laser having an integral cavity for frequency control may measure about 1mm in length, in contrast to lasers without the cavity and for use for instance as amplifiers which may be only 100 .mu.m in length.